samawil....we agree on something....wow!!! Great!!! Too bad you LIKE your BRG....
MSFITOY: short answer.....yes it will help if the Chip advances your timing and has its own knock sensing device. No if it does not. Pulley has nothing to do with it....in fact turbos and chargers tend to require less compression (thus less octane) than regular jobs......

 

Obviously, using too high an octane is a waste of money. But I'm still unclear whether using too high an octane can damage an engine. I did a layman's search on the web and didn't find any articles which said that.

Yet at least a couple of posts in this thread warn against using too high an octane. I doubt the posters were just making this up so I'm assuming it might be harmful under certain conditions. Can anyone clear this up?

As an aside, the API site mentioned that engines sometimes require a higher octane fuel as they age (ie, due to increased wear). Can anyone explain why?

 

911 fan......there is ABSOLUTELY no reason why higher octane can hurt an engine. this is a categorical statement of fact. some people think octane means more powerful explosions or hotter flames......nothing of the sort. Refer to my earlier post on this thread.

As to higher octane with age......this is actually true, particularly in modern cars that don't get "exercised" enough......why? well it is not a matter of wear, it is a matter of deposit formation. let's see if I can be concise.....
in the old days, gasoline was distilled (literally) and was a collection of short chain hydrocarbons....these burn up easily and leave no ash or residue. Fast forward 40 years, gasoline is made up with other parts of the hydrocarbon chain and these are loong chained hydrocarbons and they don't burn as easily and they leave a residue. At firts the residue collects on the intake valves....this was found to be TERRIBLE for emissions, never mind performance. Enter the EPA....thou shalt use additives to prevent intake valve deposits......oil companies comply.....guess where the deposits end? On top of the piston and in the combustion chamber, where they harden, essentially increasing the compression ratio of the engine and actually promoting "pinging" cuz some of these deposits act like embers and start up explosions by themselves......at that point, no amount of octane will help you. Only a tear down, removal of deposits and good as new......

 

>>>>Be careful about octane ratings, there is a point of 'bad' returns. Most of the race fuels you will find at your local gas station runnin the 104 to 108 range, this is way too high for your mini, in fact it's way too high even for a JCW Mini. You should never put more thatn 98 octane in your mini, unless you have a turbo charged 300+hp car. Too high of an octane will burn your engine up!
>>>>Interestingly enough my local Sunoco station has 93 octane and its actaully cheaper per gallon than high test (usally 90 to 92octane) from any other station in town (Danbury, CT)
>>
>>Just so we are clear about what octane means........
>>Octane is a measure of the anti detonation characteristics of the gasoline, in other words, how UNEXPLOSIVE it is under pressure.
>>the "knock" we hear from engines running on low octane number is the actual crashing of two flame fronts, one started by the spark and the other started by the pressure....they collide and the resulting "bang" turns into a "ping" when it gets to your ear. If violent and repetitive enough, these innocuous pings will tear parts of your piston off its surface and eventually melt it.
>>In short....120 octane fuel will do nothing harmful to your engine, though it is liable to hurt your wallet. And yes I do work in the industry and yes I know what I am taking about. 120 octane fuel will allow you to time the engine to within an inch of its life (right on kenchan) but it cannot possibly harm it. :smile:


I wouldn't go that far. I don't think it'd harm the MINI, but if you were to run that gas in a stock Ford Focus (not SVT) you're probably doing a world of hurt to the exhaust valves. They're known to run badly on high test.

 

>>Sooooo...what's the verdict then? If 104 won't do any harm, will it do any good for a pullyed Mini with ECU remap like Unichip or powerchip? Will the ECU further lean the mixture to allow more power?
>>
>>Thanks

Yes and yes. It'll make a lean mixture with lots of advance on the UNICHip with the "B" map active.

 

Update - I just finished the first tank of premium fuel after mistakenly having filled up with regular fuel the last time.

I got the worst mileage ever -- less than 20 MPG -- from this last (premium) tank-full! I normally get 22-24.

I don't know whether to blame this on the ECU adapting back to premium fuel or to my exuberant driving after the normal MCS performance returned!

My guess is that the ECU adapts very quickly so it must have been my driving!

 

Accurate fuel economy testing on vehicles and real life conditions is incredibly hard. One of the biggest variables is a little known part, the nut behind the wheel..... :smile:

 

"Sanddan is on the right track here. "

So is MrBean.

The higher the octane, the slower the fuel burns. Fuel does not explode in the combustion chamber, it burns. Not counting nitro. :smile:

 

Just to clarify what some others have said. Higher octane fuel does NOT contain more power than lower octane fuel, in fact the btu rating is less. Of course diesel fuel has a higher btu content than gasoline, but that is a different subject. You will not melt parts in your engine by running higher octane fuel, because the ignition temperature will not be any higher, and may in fact be lower than with the fuel for which your car was designed. What may happen with higher octane, since it burns more slowly, and less completely, is that you may increase the amount of deposits that build up in the engine. That is why many people that have run higher octane fuels in their cars than were recommended find that after a time they MUST run the higher octane fuel. The deposits in the engine have effectively raised the compression ratio to the point that the higher octane is required. Bottom line, use the fuel that your car was designed to burn. Never go to a lower octane number and resist the urge to go to a higher number. There will be no performance benefit and you may increase the deposits in your engine. If the engine has been modified to take advantage of higher octane fuel, then you will need to use it, but the increase in power comes from the engine modifications, not from the fuel.
I hope that helps clear things up.

 

Debating point.......from someone who currently is in the business of fuels, fuel additives, fuel composition, fuel blending...ad infinitum.....

There is absolutely no correlation whatsoever between higher octane and deposits formation. None, zip, nada.
Deposit formation is a function of the length of the hydrovarbon being used. Think of it as a whole mess of pieces of chalk......when you throw a long stick to the ground, it breaks into pieces and bounces of......throw a little piece and more likely than not, it will not break and it will hardly bounce. Those are akin to "cracked" hydrocarbon molecules, which make upa goodly portion of the gasoline pool these days. Also any "ols" like ethanol are horrible deposit makers. MTBE was thought great cuz it was a great oxigenate and it was the least deposit forming of them.

 

Follow up...

It's been several weeks since I mistakenly filled up my MCS with regular unleaded fuel.

I've gone through many tank fulls of premium unleaded since that incident. I'm consistently getting worse gas mileage after the incident (19-20 MPG) than before (22-24 MPG). Same driving patterns, driving style, etc.

I can't think of any mechanical reasons -- I'm wondering if it could be related to the ECU somehow...

Any explanations?

 

I've been using regular unleaded for about 6 months now, no change in performance and my gas mileage is actually a little better. I don't think your problems are at all octane related as the MINI's are given regular fuel to get them off the boats and on and off the trucks. Most dealerships use regular unleaded as well. Perhaps you just got some dirty gas.

 

Believe it or not, MPG is VERY difficult to measure accurately. To give you a sense, the WIND will move your MPG up or down up to 50% or more! I am thinking there is nothing wrong and if there is, it has nothing to do with the gas. Of course my main motto is if it ain't broke, don't fix it......

 

When you try to calculate MPG over only one tank of gas two very large variables are how full the tank was initially and how full you fill it a the end of the testing period.

 

Amen on the tank level. On Super Truck I get to attempt to measure MPG's over long distances with different types of fuel and one thing I have learned is to make sure I fill it to the absolute and total gills (I know it is not good citizenship but good data is better than bad data) so that I can be somewhat assured that the level is the same. Even then, there is probably a gallon or a half a gallon variable as not all the air comes out right away. If you had the time you'd let the vehicle sit for ten minutes AFTER you thought you had filled it to the gills, and you would find ANOTHER gallon's worth of volume. At any rate, at work we use flow meters to attempt to measure and they come pretty close. Also, the Society of Automotive Engineers (SAE) has a WHOLE PROCEDURE on properly measuring FE. It involves two identical vehicles, two drivers a set route, the works.......

 

Yes, I agree, there are several possible sources of error in a single measurement.

However, it seems to me that if you evaluate mileage over several tank fulls (ie, total miles travelled divided by total gallons filled), you average out those errors to a useful extent.

I'm surprised by some of pocketrocketowner's comments though. Like wind affecting MPG by 50% and having a gallon's worth of air trapped in the tank. I'm not doubting it (well, maybe just a little) -- but I am surprised!

It's interesting how a seemingly simple thing like computing gas mileage can be so complicated to accomplish accurately.

 

OK, I'll give you an explanation and ask you to do something for me.


a) wind....the laws of physics dictate that wind resistance CUBES (as in 2x2X2) with speed. This is why if your MC has 100 HP and weighs 2500 pounds (25 hp per pound) and can go a max of 150 MPH it DOES NOT FOLLOW that an Indy car that has 1000 HP and weighs 1000 pounds (1 pound per HP) the Indy car can go 25 times 150 MPH. With any luck at all, it might reach 250 MPH........that is the wind resistance stopping it, regardless of how much smaller frontal area it has, the wind resistance is incredibly stronger.

b) go to the gas station, fill up your car as normal (until the nozzle clicks off)
Now get your patient hat on and slooowly squeeze the nozzle trigger and continue filling, never mind how many times it clicks off......keep squeezing and filling. I am betting you will be able to put in at least two more gallons until you absolutely, positively can see the gasoline at the edge of the filler neck. Now still with your patient hat on, leave the cap off, and sit there for ten minutes, and then look, You will not see the gas, most of the air in the tank will now be gone and I am guessing you will be able to put in at least another half a gallon.

 

911Fan: A recent change in weather as the seasons are changing can attribute to the mpg differences too. Whether it's being more warmer, cooler, dryer, or just humid, these all play a role and things like this, among others, are just out of our hands, hehe. I've always heard that (and makes sense) that during weather (read winter time) equates to a slight drop in gas mileage and in the heat it goes back up. Unless it's becoming winter on your side of the world, or you know, at least has been generally colder lately, i'm not sure if it really could be the weather, but it's just another dang variable, hehe.